Green stripping and recycling method for positive electrode material of waste lithium iron phosphate battery

Abstract

The invention relates to the technical field of lithium ion battery material recovery, in particular to a green stripping recovery method of a waste lithium iron phosphate battery positive electrode material. The method comprises the following steps: discharging and disassembling the waste lithium iron phosphate battery to obtain a positive pole piece; a hydrogen bond acceptor, a hydrogen bond donor and water are mixed, heated and stirred, the eutectic solvent is obtained, the hydrogen bond acceptor is inorganic salt capable of generating sulfate radical, nitrate radical, phosphate radical, carbonate radical or ammonium radical, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, n-butylamine, N-ethylethylenediamine, 1-propanethiol and diallyl sulfide; and soaking and stripping the positive pole piece in the eutectic solvent to obtain the stripped and recycled positive pole material. According to the method, stripping and recycling of the positive electrode material are achieved, and the stripped and recycled positive electrode material is complete in structure, high in purity and good in electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery material recycling, and particularly to a green stripping and recycling method for the cathode material of waste lithium iron phosphate batteries. Background Art

[0002] Lithium-ion batteries have been widely used in the field of energy storage and conversion due to their many advantages such as long service life, high energy efficiency, and environmental friendliness. However, the service life of lithium-ion batteries is about 8 - 10 years, so a large number of waste lithium-ion batteries are generated. Waste lithium-ion batteries contain rich key metals (such as lithium, cobalt, nickel, manganese, etc.), and their content is much higher than that of natural minerals. How to efficiently recycle these waste lithium-ion batteries has become an important research topic, especially the cathode material among them. For this reason, various methods have been adopted to recycle waste cathode materials, such as mechanical crushing, pyrometallurgy, and hydrometallurgy, etc. However, these methods have problems such as low recovery rate, high energy consumption, and environmental pollution.

[0003] Direct recycling is an emerging recycling method that directly repairs the battery's electrode materials and restores their performance, avoiding complex recycling processes. This method can effectively simplify recycling steps, reduce costs and reduce environmental pollution. However, due to the strong adhesion between the positive electrode material and the current collector, the direct recycling process is hindered to a certain extent. Therefore, it is necessary to perform pretreatment to separate the positive electrode material and the current collector. Common stripping methods usually include: (1) Mechanical stripping, such as grinding, crushing, screening, etc. This method is environmentally friendly and can be used on a large scale, but it will lose a lot of active substances and leave a lot of impurities. (2) High-temperature calcination stripping, treating the positive electrode at high temperature to decompose or inactivate the organic binder, thereby achieving the purpose of separating the positive electrode material and the current collector. This method has the characteristics of short process, high productivity and mature technology, but it also has the defects of high energy consumption and high emissions, and high-temperature calcination may also destroy the structure of the positive electrode active material. (3) Acid / base treatment stripping, by using strong acid or strong base to dissolve the current collector, the current collector and active material can be quickly separated. However, this process will produce a large amount of hydrogen, the active substances will also dissolve into the solution, and a highly polluting waste liquid will be produced. (4) Organic solvent stripping: Some organic solvents can dissolve PVDF (polyvinylidene fluoride) according to the principle of "like dissolves like", and then strip the positive electrode material and current collector, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAC), which has little effect on the original structure of the active material. However, due to the limited solubility of PVDF in these organic solvents, a large amount of solvent is often required to dissolve it, and these solvents are also highly toxic, so it is difficult to put them into practical use. It can be seen that the above-mentioned traditional stripping methods have problems such as introducing impurities, polluting the environment, destroying the structure or high cost, making it difficult for their practical application to be further developed.

[0004] As a new type of green stripping solvent, deep eutectic solvent (DES) has shown great potential in the field of cathode material recycling in recent years. DES is usually composed of renewable organic acids and amines, and has the advantages of low energy consumption, low toxicity, biodegradability, and low damage to the results, which makes it have significant advantages in environmental protection and sustainability. However, DES also faces some challenges in the process of cathode material recycling, including complex technology, high viscosity, regeneration problems, and scale challenges.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a green stripping and recycling method for waste lithium iron phosphate battery positive electrode materials, aiming to solve the problems of complex technology and high viscosity in the positive electrode material recycling process of the existing DES.

[0007] The technical solution of the present invention is as follows: The present invention provides a green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries, which includes the following steps: S1. Discharge and disassemble the waste lithium iron phosphate batteries to obtain the positive electrode plates; S2. Mix, heat and stir a hydrogen bond acceptor, a hydrogen bond donor and water to obtain a deep eutectic solvent. The hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate or ammonium radical, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, n-butylamine, N-ethylethylenediamine, 1-propanethiol and diallyl sulfide; S3. Immerse and strip the positive electrode plates in the deep eutectic solvent to obtain the stripped and recycled positive electrode material.

[0008] Optionally, the hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate or potassium carbonate.

[0009] Optionally, the hydrogen bond acceptor is ammonium sulfate and the hydrogen bond donor is n-butylamine.

[0010] Optionally, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1-5:1-5, and the mass percentage of water in the deep eutectic solvent is 10 wt%-40 wt%.

[0011] Optionally, in step S2, the heating temperature for mixing, heating and stirring the hydrogen bond acceptor, the hydrogen bond donor and water is 10°C-150°C, and the stirring time is 5 min-60 min.

[0012] Optionally, in step S3, the mass ratio of the positive electrode plates to the deep eutectic solvent is 1:10-50.

[0013] Optionally, in step S3, the stripping temperature for immersing and stripping the positive electrode plates in the deep eutectic solvent is 10°C-90°C, and the stripping time is 1 min-60 min.

[0014] Optionally, in step S3, the step of immersing and stripping the positive electrode plates in the deep eutectic solvent to obtain the stripped and recycled positive electrode material specifically includes: Immerse and strip the positive electrode plates in the deep eutectic solvent, and obtain the stripped and recycled positive electrode material through screening, cleaning and drying.

[0015] Beneficial effects: The present invention provides a green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries. By using a eutectic solvent made of specific hydrogen bond acceptors, hydrogen bond donors, and water to soak and strip the positive electrode sheets of waste lithium iron phosphate batteries, the stripping and recycling of the positive electrode material are achieved. The stripped and recycled positive electrode material has a complete structure and high purity, can be directly used as the positive electrode material of lithium iron phosphate batteries, and exhibits good electrochemical performance. At the same time, the method of the present invention has the advantages of simple operation, high stripping efficiency, small damage to materials, no additional waste generation, recyclability, significant economic benefits, and environmental friendliness, and has high practical value. Brief Description of the Drawings

[0016] Figure 1 It is a flowchart of a green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries provided by the present invention.

[0017] Figure 2 It is an ICP characterization diagram of the stripped and recycled positive electrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the positive electrode sheets of brand-new unused lithium iron phosphate batteries.

[0018] Figure 3 It is an XRD characterization diagram of the stripped and recycled positive electrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the positive electrode sheets of brand-new unused lithium iron phosphate batteries.

[0019] Figure 4 It is a rate performance diagram of the stripped and recycled positive electrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the positive electrode sheets of brand-new unused lithium iron phosphate batteries, respectively, when used as the positive electrode of button batteries.

[0020] Figure 5 It is a comparison diagram of waste lithium iron phosphate positive electrode materials after 20 minutes of soaking and stripping in Example 2 and Comparative Example 4. Detailed Embodiments

[0021] The present invention provides a green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries. To make the purpose, technical solution, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] As Figure 1 shown, the embodiment of the present invention provides a green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries, which includes the steps of: S1. Discharge and disassemble the waste lithium iron phosphate battery to obtain the positive electrode sheet; S2. Mix a hydrogen bond acceptor, a hydrogen bond donor and water, and heat and stir the mixture to obtain a deep eutectic solvent. The hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate or ammonium radical, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, n-butylamine, N-ethylenediamine, 1-propanethiol and diallyl sulfide; S3. Immerse the positive electrode sheet in the deep eutectic solvent for soaking and stripping to obtain the stripped and recycled positive electrode material.

[0023] The embodiment of the present invention provides a green stripping and recycling method for the positive electrode material of a waste lithium iron phosphate battery. First, the waste lithium iron phosphate battery is discharged and disassembled to obtain a positive electrode sheet. Then, a specific hydrogen bond acceptor, hydrogen bond donor and water are formulated into a deep eutectic solvent (DES), and the positive electrode sheet obtained by the discharge and disassembly treatment is immersed in the deep eutectic solvent for stripping and recycling, so as to realize the complete stripping of the lithium iron phosphate positive electrode material. The innovation of the embodiment of the present invention mainly lies in the use of a deep eutectic solvent made of a specific combination of a hydrogen bond acceptor, a hydrogen bond donor and water. The whole process avoids the use of harmful corrosive chemicals such as strong acids and strong bases, ensures the integrity and purity of the recycled positive electrode material, and the addition of water can also control the viscosity of the deep eutectic solvent and reduce the preparation cost, showing a high economic advantage. Compared with the traditional stripping process (such as high-temperature calcination, organic solvents, etc.), the product obtained by this process has better structural integrity and sample purity, and has better electrochemical performance when directly used as the positive electrode material of a lithium iron phosphate battery. In addition, the method of the embodiment of the present invention also has the advantages of simple operation, high stripping efficiency, small damage to materials, no additional waste generation, recyclability, significant economic benefits and environmental friendliness, and has high practical value.

[0024] In the embodiment of the present invention, the positive electrode sheet of the waste lithium iron phosphate battery is soaked and stripped by using a specific combination of deep eutectic solvents. The hydrogen bond acceptor in the DES dissociates into H + / OH - and reacts with Al2O3 on the surface of the aluminum foil to further destroy the interfacial bonding force between the aluminum foil and the positive electrode material. In addition, since the DES binds to PVDF by hydrogen bonds, the PVDF on the surface of the positive electrode material is also inactivated. Under the combined action of these two effects, the aluminum foil and the positive electrode material are quickly separated. Based on the above effects, using the specific combination of deep eutectic solvents described in the present invention can simultaneously obtain a high-purity and structurally stable separated lithium iron phosphate layer material and an intact and undamaged aluminum foil.

[0025] In the embodiments of the present invention, inorganic salts capable of generating sulfate, nitrate, phosphate, carbonate or ammonium are used as hydrogen bond acceptors, which have strong hydrogen bond acceptor ability and can form stable hydrogen bonds with hydrogen bond donors, thus effectively reducing the melting point of the deep eutectic solvent and enabling it to form a uniform and transparent liquid at a lower temperature, facilitating subsequent stripping operations; and these inorganic salts usually have high chemical stability, environmental friendliness and availability. While urea, thiourea, tetraethylenepentamine, n-butylamine, N-ethylenediamine, 1-propanethiol and diallyl sulfide are used as hydrogen bond donors, and the electronegativity difference between the hydrogen bond donor atoms (such as nitrogen, phosphorus, sulfur atoms, etc.) and hydrogen atoms in these materials is large, capable of forming stable hydrogen bonds; and these materials are also often used as various additives, fertilizers and drugs, having the advantages of low cost and small environmental impact. In addition, the addition of water is beneficial to reducing the viscosity of the DES, thereby enhancing the permeability and fluidity of the deep eutectic solvent, improving the stripping effect, and at the same time reducing the cost. Formulating the hydrogen bond acceptor, hydrogen bond donor and water into a deep eutectic solvent has advantages such as a stable hydrogen bond structure, low melting point and viscosity, can quickly and effectively strip the lithium iron phosphate cathode material, and also has the advantages of environmental friendliness and low cost. The deep eutectic solvent of the embodiments of the present invention can well achieve the stripping and recycling of the lithium iron phosphate cathode material.

[0026] In some embodiments, the hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate or potassium carbonate.

[0027] In some embodiments, the hydrogen bond acceptor is ammonium sulfate, potassium carbonate or tripotassium phosphate, and the hydrogen bond donor is n-butylammonium.

[0028] In some embodiments, the hydrogen bond acceptor is ammonium sulfate and the hydrogen bond donor is n-butylammonium. In this embodiment, the deep eutectic solvent obtained by mixing, heating and stirring ammonium sulfate, n-butylammonium and water has a fast stripping rate for the cathode material and can obtain a cathode material with a complete structure.

[0029] In some embodiments, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1~5):(1~5), and the mass percentage of water in the deep eutectic solvent is 10 wt%~40 wt%. Within this mass percentage range, the deep eutectic solvent exhibits low viscosity and fast stripping rate.

[0030] In some embodiments, in step S2, when the hydrogen bond acceptor, hydrogen bond donor and water are mixed and heated with stirring, the heating temperature is 10°C to 150°C (for example, it can be 10°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, etc.), and the stirring time is 5 min to 60 min (for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.). Under the conditions of the mixed heating and stirring, less energy consumption is required, the equipment requirements are lower, and better operation safety is exhibited.

[0031] In some embodiments, in step S3, the mass ratio of the positive electrode plate to the deep eutectic solvent is 1:(10 - 50). Within this mass ratio range, the stripping rate of the aluminum foil of the positive electrode plate from the lithium iron phosphate layer is faster, and a lower solution mass ratio helps to reduce costs and the generation of waste.

[0032] In some embodiments, in step S3, when the positive electrode plate is immersed in the deep eutectic solvent for soaking and stripping, the stripping temperature is 10°C to 90°C (for example, it can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc.), and the stripping time is 1 min to 60 min (for example, it can be 1 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.). Under the conditions of the soaking and stripping, the reaction conditions are milder, the required energy cost is lower, and the lower temperature also reduces the risk of high-temperature operation.

[0033] In some embodiments, in step S3, the step of placing the positive electrode plate in the deep eutectic solvent for soaking and stripping to obtain the stripped and recycled positive electrode material specifically includes: Placing the positive electrode plate in the deep eutectic solvent for soaking and stripping, and after sieving, cleaning and drying, the stripped and recycled positive electrode material is obtained.

[0034] In some embodiments, in step S1, the step of discharging and disassembling the used lithium iron phosphate battery to obtain the positive electrode plate specifically includes: Put the used lithium iron phosphate battery into a sodium chloride solution with a concentration of 5% - 10% and soak it for 48 h until it is completely discharged, then disassemble the battery to obtain the positive electrode plate. Utilize the conductivity of the sodium chloride solution to short-circuit the positive and negative electrodes of the battery to achieve the purpose of discharging.

[0035] The following further illustrates the present invention through specific embodiments.

[0036] Example 1 This example explores the structural damage of the green stripping and recycling method of the positive electrode material of the used lithium iron phosphate battery provided by the present invention. In order to avoid the interference of various structural damages already existing in the used lithium iron phosphate positive electrode material, this example selects the positive electrode plate of a brand-new unused lithium iron phosphate battery purchased on the market for demonstration, as follows: (1) Mix ammonium sulfate (hydrogen bond acceptor) and n-butylamine (hydrogen bond donor) with a molar ratio of 2:1, and water with a mass percentage of 40.0 wt% in the deep eutectic solvent at 25 °C, and heat and stir for 10 min to obtain the deep eutectic solvent; (2) Cut the positive electrode plate of the brand-new unused lithium iron phosphate battery into a size of 2 cm 2 . According to the mass ratio of the positive electrode plate to the deep eutectic solvent of 1:20, place the positive electrode plate in the deep eutectic solvent and soak and strip it at 40 °C for 10 min. The aluminum foil is completely separated from the lithium iron phosphate positive electrode material. Then fish out the aluminum foil and dry it, and then screen and wash the remaining mixture, collect and dry the undersize to obtain the stripped and recycled positive electrode material.

[0037] Comparative Example 1 High-temperature calcination stripping and recycling of the positive electrode material: Use the same brand-new unused lithium iron phosphate battery positive electrode plate as in Example 1, cut it into a size of 2 cm 2 . Calcinate it at 550 °C for 3 h with a heating rate of 5 °C / min to obtain aluminum foil and the stripped and recycled positive electrode material.

[0038] Comparative Example 2 Organic solvent stripping and recycling of the positive electrode material: Use the same brand-new unused lithium iron phosphate battery positive electrode plate as in Example 1, cut it into a size of 2 cm 2 . Put it into the NMP solution and stir gently at 100 °C for 24 h. After the stripping process is completed, through screening, washing and drying, aluminum foil and the stripped and recycled positive electrode material are obtained.

[0039] Performance test: (1)For the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the cathode electrode sheets of brand-new unused lithium iron phosphate batteries, inductively coupled plasma (ICP) characterization and X-ray diffraction (XRD) characterization were carried out.

[0040] Figure 2 Figure for the ICP characterization of the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the cathode electrode sheets of brand-new unused lithium iron phosphate batteries (labeled as original brand-new in Figure 2 . The results show that the compositions of the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 are very close to those of the cathode electrode sheets of brand-new unused lithium iron phosphate batteries. Moreover, although the eutectic solvent used in Example 1 contains alkaline substances, it does not cause a large amount of lithium and iron in the cathode material to leach out, indicating that the eutectic solvent used in the present invention has little destructive effect on the structure of the stripped and recycled cathode materials.

[0041] Figure 3 Figure for the XRD characterization of the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the cathode electrode sheets of brand-new unused lithium iron phosphate batteries (labeled as original brand-new in Figure 3 . The results show that two impurity peaks appear at approximately 18.4° and 18.9° in the cathode material of the high-temperature calcined and stripped and recycled cathode material in Comparative Example 1, which may be related to the structural transformation of lithium iron phosphate at high temperature. However, no impurity peaks appear in the stripped and recycled cathode materials obtained in Example 1 and Comparative Example 2, indicating that the structures of the stripped and recycled cathode materials obtained by the method of the present invention and the cathode materials stripped and recycled by organic solvents are very intact, proving that the method of the present invention can well strip and recycle cathode materials.

[0042] (2)Regarding the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 as the cathode active materials to prepare cathode electrode sheets for electrochemical performance testing in button batteries, the specific steps are as follows: Preparation of cathode electrode sheets: Dissolve the binder polyvinylidene fluoride (PVDF) in the organic solvent N-methylpyrrolidone (NMP) to make a 10 wt% binder solution. Stir the stripped and recycled cathode materials obtained in Example 1, Comparative Example 1, or Comparative Example 2, the binder solution, and conductive carbon black evenly in a stirring and degassing machine according to a mass ratio of 8:1:1 to obtain a slurry, and then evenly coat the slurry on aluminum (Al) foil. After the coating process is completed, dry the aluminum foil in a forced-air drying oven at 80 °C until the organic solvent completely evaporates. Then transfer it to a vacuum drying oven and dry it at 65 °C for 12 h. Subsequently, use a manual stamping machine to stamp the aluminum foil into cathode electrode sheets with a diameter of 13 mm.

[0043] Preparation of button cells: The button cells were assembled in a glove box under an argon atmosphere, with the water and oxygen content maintained below 0.01 ppm. The battery case was of the 2032 button cell type, the separator was a Celgard 2350 composite separator, the electrolyte was a lithium-ion positive electrolyte containing 1 M LiPF6, the solvent was ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The positive electrode sheet was the positive electrode sheet obtained in the above step (1), and the negative electrode was a commercial lithium sheet. After assembling the components into button cells, the button cells were placed on a sealing machine to complete sealing, and electrochemical tests were carried out after ensuring that the electrolyte was completely absorbed by the active materials.

[0044] In addition, button cells were prepared using the same method as the above preparation of button cells, with the positive electrode sheet being the positive electrode sheet of a brand-new unused lithium iron phosphate battery. The difference was that the positive electrode sheet was the positive electrode sheet of a brand-new unused lithium iron phosphate battery, and the electrochemical performance of the button cells was tested.

[0045] The CT3001A battery test system was used to evaluate the electrochemical performance of the four prepared button cells in the voltage range of 2.5 - 4.2 V. The rate performance test of the battery was carried out by cycling 3 times at a current of 0.1C for activation, and then continuing the charge and discharge tests in the order of 0.5C, 1C, 2C, 5C, and 1C, with each rate cycle being 5 times.

[0046] Figure 4 For the stripped and recycled positive electrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the positive electrode sheet of a brand-new unused lithium iron phosphate battery (labeled as original brand-new in Figure 4 ), which were used as the rate performance diagrams of the positive electrodes of button cells respectively. According to this diagram, the discharge specific capacities of the original brand-new positive electrode sheet at 0.1C, 0.5C, 1C, 2C, and 5C were 152.18 mAh·g -1 、144.22 mAh·g -1 、135.49 mAh·g -1 、121.76 mAh·g -1 and 97.65 mAh·g -1 respectively; while the discharge specific capacities of the stripped and recycled positive electrode materials obtained in Example 1 at 0.1C, 0.5C, 1C, 2C, and 5C were 147.80 mAh·g -1 、138.24 mAh·g -1 、129.31 mAh·g -1 、117.95 mAh·g -1 and 96.51 mAh·g -1At 5C, the discharge specific capacity of the stripped and recycled cathode material obtained in Example 1 is only 1.14 mAh·g lower than that of the original brand-new cathode electrode sheet. -1 , showing excellent rate performance retention. In contrast, the rate performance of the stripped and recycled cathode material obtained in Comparative Example 1 is significantly lower than that of Example 1, and its discharge specific capacity at 5C is only 77.13 mAh·g. -1 , which may be related to the structural transformation mentioned in the aforementioned XRD test. Similarly, the discharge specific capacity of the stripped and recycled cathode material obtained in Comparative Example 2 at 5C is 88.48 mAh·g. -1 , which is also significantly lower than that of Example 1. This shows that the stripped and recycled cathode material obtained by the green stripping and recycling method of the present invention exhibits good electrochemical performance, and its performance is very well matched with that of the original brand-new cathode electrode sheet.

[0047] According to the above results, it can be seen that the composition and structure of the stripped and recycled cathode material obtained by using the method of the present invention are very close to those of the cathode material of a brand-new unused lithium iron phosphate battery, showing good structural integrity and high product purity. Moreover, compared with the cathode materials obtained by using the high-temperature calcination stripping and recycling method and the organic solvent stripping and recycling method, the stripped and recycled cathode material obtained by using the method of the present invention also has better electrochemical performance.

[0048] Example 2 This example provides a green stripping and recycling method for the cathode material of a waste lithium iron phosphate battery, specifically as follows: (1) Put the waste lithium iron phosphate battery into a sodium chloride solution with a concentration of 11.7% and soak it at normal temperature and pressure for 48 h to discharge the remaining power of the battery, and then disassemble the battery to obtain the waste lithium iron phosphate battery cathode electrode sheet; (2) Mix ammonium sulfate (hydrogen bond acceptor) and n-butylamine (hydrogen bond donor) with a molar ratio of 2:1, and water with a mass percentage of 40.0 wt% in the deep eutectic solvent at 25°C, and heat and stir for 10 min to obtain the deep eutectic solvent; (3) Cut the waste lithium iron phosphate battery cathode electrode sheet obtained in step (1) into a size of 2 cm. 2 According to the mass ratio of the cathode electrode sheet to the deep eutectic solvent of 1:20, place the cathode electrode sheet in the deep eutectic solvent and soak and strip it at 40°C for 20 min, so that the aluminum foil is completely separated from the cathode material. Then fish out the aluminum foil and dry it, and then screen and wash the remaining mixture, collect and dry the undersize to obtain the stripped and recycled cathode material.

[0049] Example 3 The same method as in Example 2 was adopted, with the only differences being that the hydrogen bond acceptor in step (2) of Example 2 was replaced with potassium carbonate, and the soaking and stripping time in step (3) was adjusted to 40 min, and finally the stripped and recycled cathode material was obtained.

[0050] Example 4 The same method as in Example 2 was adopted, with the only differences being that the hydrogen bond donor in step (2) of Example 2 was replaced with urea, and the soaking and stripping time in step (3) was adjusted to 45 min, and finally the stripped and recycled cathode material was obtained.

[0051] Example 5 The same method as in Example 2 was adopted, with the only differences being that the mass percentage of water in step (2) of Example 2 was adjusted to 20.0 wt%, and the soaking and stripping time in step (3) was adjusted to 35 min, and finally the stripped and recycled cathode material was obtained.

[0052] Comparative Example 3 The method of Comparative Example 3 was the same as that of Example 2, with the only difference being that the hydrogen bond donor in step (2) of Example 2 was replaced with ethylene glycol, and the soaking and stripping time in step (3) was adjusted to 50 min, and finally the stripped and recycled cathode material was obtained.

[0053] Comparative Example 4 The method of Comparative Example 4 was the same as that of Example 2, with the only difference being that the hydrogen bond donor in step (2) of Example 2 was replaced with lactic acid.

[0054] When comparing Example 2 with Example 3 and Example 4, although the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor of the deep eutectic solvent used in the three examples was 2:1, and the amount of water used was also the same, it only took 20 min in Example 2 to completely separate the aluminum foil from the cathode material, while it took 40 min and 45 min respectively in Example 3 and Example 4 to completely separate the aluminum foil from the cathode material. This shows that the deep eutectic solvent prepared with ammonium sulfate, n-butylamine and water in Example 2 has a faster stripping rate for the cathode material.

[0055] When Example 2 is compared with Example 5, although the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor of the eutectic solvent used in both examples is 2:1, the eutectic solvent used in Example 2 has a faster stripping rate for the cathode material. This is because the viscosity of the eutectic solvent in Example 2 at 40 °C is 4.16 cP, while the viscosity of the eutectic solvent in Example 5 at 40 °C is 4.80 cP. When the viscosity of the eutectic solvent is relatively high, it is difficult to exert its stripping effect. The higher water content in Example 2 reduces the viscosity of the eutectic solvent, and the decrease in viscosity often facilitates the penetration and flow of the eutectic solvent, which accelerates the reaction process and subsequent dynamic separation during stripping, thereby enhancing the stripping effect. In addition, the addition of water can also reduce the preparation cost of the eutectic solvent, making it have higher commercial value.

[0056] When Example 2 is compared with Comparative Example 3, although the dosage ratio of the hydrogen bond acceptor to the hydrogen bond donor of the eutectic solvent used is the same, when the hydrogen bond donor is replaced by ethylene glycol, the time required for complete stripping is extended from 20 min to 50 min. This result fully demonstrates the significant advantage of the eutectic solvent composed of ammonium sulfate, n-butylamine and water in the present invention in terms of stripping performance.

[0057] In addition, Figure 5 Figure is a comparison diagram of the spent lithium iron phosphate cathode material after 20 min of immersion and stripping in Example 2 and Comparative Example 4, where Figure 5 Figure a is the experimental result of Example 2, Figure 5 Figure b is the experimental result of Comparative Example 4. It can be clearly seen from this figure that although the spent lithium iron phosphate cathode materials in both examples achieved complete separation under the same immersion time, the eutectic solvent after stripping treatment in Example 2 presented as transparent white, while the eutectic solvent after stripping treatment in Comparative Example 4 presented as light green. This phenomenon indicates that when the hydrogen bond donor is replaced by lactic acid, more Fe 2+ is leached from the spent lithium iron phosphate cathode material. This result fully reflects the advantage of the low damage of the specific combination of eutectic solvents used in the present invention to the cathode material.

[0058] In summary, the green stripping and recycling method for the cathode material of spent lithium iron phosphate batteries provided by the present invention well realizes the stripping and recycling of the cathode material and aluminum foil. The stripped and recycled cathode material has a complete structure, high purity, can be directly used as the cathode material of lithium iron phosphate batteries, and exhibits good electrochemical performance. At the same time, the method of the present invention has the advantages of simple operation, high stripping efficiency, small damage to materials, no additional waste generation, recyclability, significant economic benefits and environmental friendliness, and has high practical value.

[0059] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or modifications can be made according to the above description, and all such improvements and modifications shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A green stripping and recycling method for the positive electrode material of waste lithium iron phosphate batteries, characterized in that, Including the steps: S1. Discharge and disassemble the waste lithium iron phosphate battery to obtain the positive electrode plate. S2. Mix, heat and stir a hydrogen bond acceptor, a hydrogen bond donor and water to obtain a deep eutectic solvent. The hydrogen bond acceptor is an inorganic salt capable of generating sulfate, nitrate, phosphate, carbonate or ammonium ion, and the hydrogen bond donor is one or more of urea, thiourea, tetraethylenepentamine, n-butylamine, N-ethylethylenediamine, 1-propanethiol and diallyl sulfide. S3. Immerse and strip the positive electrode plate in the deep eutectic solvent to obtain the stripped and recovered positive electrode material.

2. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, The hydrogen bond acceptor is potassium sulfate, sodium sulfate, copper sulfate, ammonium sulfate, ammonium bisulfate, potassium nitrate, sodium nitrate, tripotassium phosphate, iron phosphate, sodium carbonate or potassium carbonate.

3. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 2, characterized in that, The hydrogen bond acceptor is ammonium sulfate, and the hydrogen bond donor is n-butylamine.

4. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, wherein, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1-5:1-5, and the mass percentage of water in the deep eutectic solvent is 10 wt% - 40 wt%.

5. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, In step S2, the heating temperature for mixing, heating and stirring the hydrogen bond acceptor, the hydrogen bond donor and water is 10°C - 150°C, and the stirring time is 5 min - 60 min.

6. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that In step S3, the mass ratio of the positive electrode plate to the deep eutectic solvent is 1:10 - 50.

7. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that, In step S3, the stripping temperature for immersing and stripping the positive electrode plate in the deep eutectic solvent is 10°C - 90°C, and the stripping time is 1 min - 60 min.

8. The green stripping and recycling method of the cathode material of waste lithium iron phosphate batteries according to claim 1, wherein In step S3, the step of immersing and stripping the positive electrode plate in the deep eutectic solvent to obtain the stripped and recovered positive electrode material specifically includes: Immerse and strip the positive electrode plate in the deep eutectic solvent, and obtain the stripped and recovered positive electrode material through screening, cleaning and drying.

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